Kay Rasmus Nielsen (1886–1957) was a Danish illustrator and stage designer, born in Copenhagen. He gained recognition during the early 20th century, a period often referred to as the Golden Age of Illustration. His parents were the actors Oda Nielsen and Martinus Nielsen.
Nielsen created illustrations for Anglo-American gift books, a genre popular in the early 20th century. His work included designs such as the "Sultan's Official Divan in Aladdin" (1916) for stage, and illustrations like "Shenreddin and Nureddin in Egypt". Later in his career, he contributed story sketches and illustrations for Disney, notably for the "Night on Bald Mountain" sequence in the 1940 animated film Fantasia, and early conceptual work for The Little Mermaid.
